Nonaqueous cell with improved thermoplastic sealing member

ABSTRACT

An electrochemical battery cell with an improved thermoplastic sealing member. The seal member is made from a thermoplastic resin comprising polyphthalamide or impact modified polyphenylene sulfide. The seal member provides an effective seal vent over a broad temperature range and has a low electrolyte vapor transmission rate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/682,223, filed Oct. 9, 2003, entitled Nonaqueous Cell withImproved Thermoplastic Sealing Member, currently pending, which isincorporated herein by this reference.

BACKGROUND

This invention relates to an electrochemical battery cell with anonaqueous organic solvent electrolyte and an improved thermoplasticsealing member.

Nonaqueous battery cells are cells that contain essentially no water.The cell electrode materials and electrolyte are carefully manufactured,dried and stored prior to cell manufacturing to maintain the amount ofwater in those components at typically no more than tens or hundreds ofparts per million. Those manufacturing processes in which cell internalcomponents are exposed to the air are generally performed in a dry boxor a dry room. These measures are necessary because of the highreactivity of one or more of the cell ingredients with water. Organiccompounds are often used as electrolyte solvents in nonaqueous cells.Examples of nonaqueous cells that contain such organic solvents includelithium and lithium ion cells, though other types of nonaqueous cells,containing other materials that are highly reactive with water areknown.

Batteries containing nonaqueous cells are becoming increasingly popularas power sources for electronic devices. Though they are often morecostly than common aqueous cells, nonaqueous cells can have manyadvantages because of the natures of materials used. These advantagesinclude high energy density, high capacity at low temperatures, lowweight and excellent shelf life over a broad range of temperatures. Manynonaqueous cells also have high electrode interfacial surface areadesigns that make them especially well suited for high power (includinghigh current and low resistance) discharge, and the general trend inpower requirements for electronic devices has been toward higher andhigher power. Some of the types of devices for which high capacity onhigh power discharge is particularly important include photoflashdevices (flash units and cameras with internal flash capability),digital still cameras, video cameras, personal digital assistant devicesand portable computers.

The ability to withstand extreme temperature conditions, includingthermal cycling and thermal shock between high and low temperatures, isbecoming more important for nonaqueous cells, particularly lithium andlithium ion cells larger than button cells.

Requirements for lithium and lithium ion cells to tolerate extremetemperature conditions without seal degradation resulting in salting,leakage, excessive weight (electrolyte) loss, venting at low internalcell pressures and excessive capacity loss are increasing. This is truefrom the standpoint of both the severity of the conditions that thecells must tolerate and the number and types of applications for whichsuch requirements are being set. Cells with thermoplastic seal membersmade according to the prior art are not able to meet all of theserequirements in certain cell types, particularly cells with electrolytesolvents having low boiling points.

A wide variety of cell designs have been used for nonaqueous cells. Thetype of design is dependent in part on the size of the cell, the type ofelectrode and electrolyte materials used in the cell and the powerrequirements of the devices to be powered by the cell. Because thecathode/electrolyte materials are so reactive, the designs for largeliquid cathode lithium cells (e.g., lithium-sulfur dioxide (Li/SO₂) andlithium-thionyl chloride (Li/SOCl₂)) often have housings in which metalcomponents are hermetically welded, and glass seals are used to sealmetal components that must be electrically insulated and to seal smallapertures in the housings. These types of housings tend to be expensivedue to the materials and the manufacturing processes and equipmentrequired.

Other means can be used to seal the cells. Because of the relatively lowcost and ease of manufacture, it can be desirable to use thermoplasticseal members between rigid housing components. For example, athermoplastic gasket or grommet can be compressed between the inside topedge of the cell container (e.g., a steel can) and the periphery of thecover closing the open top of the can, forming a seal to keep theelectrolyte within the cell housing and to keep water out.

A thermoplastic seal member can also be used to seal an aperture in thecell housing. For example, the thermoplastic seal member may be in theform of a plug sealing a small hole in the cell cover. Electrolyte maybe dispensed into the cell after the cover has been assembled to thecan. In another example, the plug may be a rigid material, such as aglass or metal ball, with a thermoplastic seal member in the form of abushing between the inner surface of the aperture and the ball. In theseexamples, the thermoplastic plug or the ball and bushing may alsofunction as a pressure relief vent for the cell.

FIG. 1 shows an example of a cylindrical lithium cell design that hasbeen used for Li/FeS₂ and other lithium cell types. It has twothermoplastic seal members—a gasket sealing a cover in the open end ofthe can and a bushing sealing an aperture in the cell cover. Boththermoplastic seal members provide a compressive seal. Since the can andcover are electrically connected to opposite electrodes within the cell,the gasket also provides the necessary electrical insulation. Thebushing and a vent ball comprise a pressure relief vent for the cell.When the internal cell pressure exceeds a predetermined abnormally highlevel, the vent ball (or the ball and bushing) are forced out of thecover, leaving an opening through which pressure is released. Cellssealed with both a gasket between the can and cover and a pressurerelief vent comprising a bushing and vent plug disposed in an aperturein the cell cover are disclosed in U.S. Pat. Nos. 4,329,405 (issued May11, 1982), 4,437,231 (issued Mar. 20, 1984), 4,529,673 (issued Jul. 16,1985), 4,592,970 (issued Jun. 3, 1986), 4,927,720 (issued May 22, 1990)and 4,931,368 (issued Jun. 5, 1990) and 5,015,542 (issued May 14, 1991),the entire disclosures of which are incorporated herein.

Thermoplastic seal members are also used in other types of cells,including aqueous electrolyte cells such as common consumer type aqueouszinc-manganese dioxide (Zn/MnO₂), nickel-cadmium (Ni/Cd) andnickel-metal hydride (NiMH) cells.

For any cell type, the seal member material and design must be such thata suitable seal is maintained for an acceptable period of time and underthe temperature conditions that the cell is expected to withstand duringtransportation, storage and use. Common characteristics of a good sealmember include stability of the material in the internal cell andexternal environments, impermeability to the liquids and gases that areto be sealed within or outside the cell, and the formation andmaintenance of a complete seal path (i.e., with no voids or gaps) ateach seal interface.

For thermoplastic seal members which form a compressive seal, the sealmember must be sufficiently compressed to achieve a good seal, andsufficient compression must be maintained for the desired time.Thermoplastic materials under compressive stress tend to relieve thatstress. This is referred to as stress relaxation or cold flow of thematerial. Thermoplastic materials tend to stress relax more at highertemperatures, thereby reducing the time that sufficient compression canbe maintained. Temperature also affects the compression of thermoplasticseal members in another way. Different materials will expand andcontract by different amounts in response to increases and decreases,respectively, in ambient temperature. In a cell with a thermoplasticseal member forming a compressive seal between more rigid components(e.g., a metal can and a metal cover), it is generally desirable for thegasket and rigid components being sealed to expand at close to the samerate in order to maintain sufficient gasket compression over thegreatest temperature range possible.

Thermoplastic materials and seal designs suitable for nonaqueous cellseal members are more limited than for aqueous cell seal members.Because active materials in the cell are very reactive with water, theseal members must have a higher degree of impermeability to water, andsome common materials for aqueous cell seal members are not suitable.Nonaqueous cell seal members must also have a low vapor transmissionrate for the electrolyte solvents. Since the vapor transmission rate ofthermoplastic material is generally dependent in part upon the vaporpressure of the solvent, low vapor transmission rates are generally moredifficult to achieve for nonaqueous cells whose electrolytes containethers or other organic solvents with low boiling points. The greaterthe ratio of the effective cross sectional area of the seal member tothe internal volume of the cell, the more important the electrolytesolvent and water transmission rates.

For use in some devices, such as those that may be used in automobileengine compartments and some outdoor environments, batteries must becapable of withstanding very high or very low temperatures.Electrochemical characteristics of some lithium and lithium ion cellsmake them desirable for use at such temperature extremes. However, sealmembers used in cells intended for such applications must be able tomaintain an acceptable seal at those extreme temperatures. Theimportance of resistance to the effects of temperature extremes isbecoming more important.

Polypropylene (PP) is commonly used a material for lithium cell (e.g.,Li/MnO₂ and Li/FeS₂) gaskets. Gaskets have been made with otherthermoplastic materials for the purpose of improving the ability of thecell to withstand high temperatures than with PP.

Sano et al. (U.S. Pat. No. 5,624,771) disclose the use of polyphenylenesulfide (PPS), rather than PP, as a gasket material for a lithium cellto improve resistance of the cell to high temperatures. PPS was used toreduce gasket deformation due to cold flow under the high loadconditions the gasket was subjected to in the cell.

In U.S. Pat. No. 5,656,392, Sano et al. disclose thermoplastic syntheticresins, PPS and tetrafluoride-perfluoroalkyl vinylether copolymer (PFA),as suitable for making a gasket for a cell that is useable at hightemperatures and solves conventional problems caused by long-period useand/or storage. Also disclosed are the addition of a glass fiber fillerto the resin to extend the stability of the gasket configuration and theaddition of polyethylene (PE) and/or polypropylene (PP) to extend thetemperature range that can be tolerated by the cells on a cyclic thermalshock test. However, gaskets containing more than 10 weight percentglass fiber were undesirable because cells made with such highly filledthermoplastic materials leaked on a temperature cycling test. Theaddition of more than 10 weight percent of PE and/or PP was alsoundesirable because of cell leakage and a continuously usabletemperature of less than 150° C. for the gasket.

Both U.S. Pat. No. 5,624,771 and U.S. Pat. No. 5,656,392 teach that highboiling point solvents such as γ-butyrolactone (boiling point 202° C.)and propylene carbonate (boiling point 241° C.) can be used aselectrolyte solvents to achieve the desired high temperature cellperformance and still maintain practical low temperature (−20° C.) celloperation in a Li/(CF)_(n) coin cell. However, lithium cells withelectrolytes containing a large amount of low boiling point solvents donot perform as well on high power discharge, which can be a disadvantagein larger cells intended for use in high power discharge applications.

In U.S. Pat. No. 6,025,091 Kondo et al. disclose a cell with a metal cansealed with a metal terminal cap and a gasket comprising polybutyleneterephthalate (PBT). The gasket material can be PBT alone, PBT mixedwith another polymer or PBT reinforced with inorganic materials such asglass fibers, glass beads and certain organic compounds. Kondo et al.disclose that the invention solves the problems of creeping and crackingof the gasket material when the cell is exposed to high temperature. Thepreferred cell type was a secondary cell, either with an alkaline ornonaqueous electrolyte (e.g., a lithium ion cell). A particularlypreferred electrolyte contained LiCF₃SO₃, LiClO₄, LiBF₄ and/or LiPF₆dissolved in a mixed solvent comprising propylene carbonate or ethylenecarbonate and 1,2-dimethoxyethane and/or diethyl carbonate and1,2-dimethoxyethane and/or diethyl carbonate.

In the mid-1980's Union Carbide Corp. also manufactured a ⅓ N sizeLi/MnO₂ cell (Type No. 2L76) with a gasket made from PBT (GAFITE® fromGAF Chemicals). These cells had a spiral wound electrode design andcontained an electrolyte with comprising a mixture of lithiumperchlorate and lithium trifluoromethanesulfonate salts in a solventcontaining 50 volume percent each of propylene carbonate and1,2-dimethoxyethane.

The prior art teaches that the ability of cells to withstand a widerange of temperatures, especially high temperatures, can be improved byusing gaskets made from materials that maintain dimensional stabilityand do not crack under extreme temperature conditions. The problem ofreducing the rate of transmission of electrolyte solvent through thegasket is not addressed. This problem is generally greater at highertemperatures and with more volatile organic solvents with lower boilingpoints, such as ethers.

Accordingly, battery cells with improved thermal tolerancecharacteristics, with little or no adverse effects on other cellcharacteristics, are desired. Therefore, an object of the presentinvention is to provide an economically made electrochemical batterycell, with a seal member made from one or more thermoplastic resins,having improved thermal tolerance characteristics, good resistance toloss of electrolyte and entry of water and little degradation inperformance after long-term storage.

SUMMARY

The above objects are met and the above disadvantages of the prior artare overcome by an electrochemical battery cell of the presentinvention.

It has been discovered that the seal effectiveness of a cell with athermoplastic seal member made from a polymeric resin comprisingpolyphenylene sulfide blended with from greater than 10 to no greaterthan 40 weight percent of an impact modifier or with polyphthalamide canprovide reduced electrolyte vapor transmission through and around theseal member.

Accordingly, in one aspect the present invention is directed to anelectrochemical battery cell comprising a housing comprising a metalcontainer with at least one open end and at least a first metal coverdisposed in the at least one open end of the container, a positiveelectrode, a negative electrode, a separator disposed between thepositive and negative electrodes, an electrolyte, and a firstthermoplastic seal member made from a polymeric resin comprising atleast one member selected from the group consisting of polyphenylenesulfide blended with from greater than 10 to no greater than 40 weightpercent of an impact modifier and polyphthalamide.

Another aspect of the present invention is an electrochemical batterycell comprising a housing comprising a metal container with an open endand a metal cover disposed in the open end of the container; a positiveelectrode; a negative electrode; a separator disposed between thepositive and negative electrodes, an electrolyte comprising a solute,the solute comprising lithium and iodide ions, dissolved in a nonaqueoussolvent; and a thermoplastic seal member disposed between the metalcontainer and the metal cover. The thermoplastic seal member is madefrom a polymeric resin comprising at least one member selected from thegroup consisting of polyphenylene sulfide blended with from greater than10 to no greater than 40 weight percent of an impact modifier andpolyphthalamide.

Yet another aspect of the present invention is an electrochemicalbattery cell comprising a housing comprising a metal container with anopen end and a metal cover disposed in the open end of the container, apositive electrode comprising iron disulfide; a negative electrodecomprising metallic lithium; a separator disposed between the positiveand negative electrodes; an electrolyte comprising a solute dissolved ina nonaqueous organic solvent, the solute comprising lithium and iodideions and the solvent comprising at least 80 volume percent of one ormore ethers, each having a boiling point no greater than 90° C.; and athermoplastic seal member disposed between the metal container and themetal cover. The thermoplastic seal member is made from a polymericresin comprising at least one member selected from the group consistingof polyphenylene sulfide blended with from greater than 10 to no greaterthan 40 weight percent of an impact modifier and polyphthalamide.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

Unless otherwise specified, the following definitions and methods areused herein:

-   -   aperture means an opening in a material that extends from an        area within one surface to an area within an adjacent surface of        the material; an open end of a container such as a can or a tube        is not an aperture;    -   creep strain rate is determined by Dynamic Mechanical Analysis        using a Tritec 2000 DMA from Triton Technologies, Ltd., UK, at a        test temperature of 85° C.; resin is compression molded to form        a 0.25 mm thick film and cut to a width of 2.3 mm; the initial        gauge length is 2.0 mm, a constant tensile force of 6 N is        applied to give a constant tensile stress of 10,000 kPa;    -   crimp release pressure means the internal cell pressure at which        the cell housing deforms sufficiently to break the        container/seal member/cell cover seal and release pressure from        the cell;    -   coefficient of thermal expansion is determined in the flow        direction between 50° C. and 90° C. according to ASTM E831 and        expressed in cm/cm/degree Celsius;    -   heat deflection temperature is determined at 18.56 kg/cm² (264        pounds per square inch (psi)) according to ASTM D648 and        expressed in degrees C.;    -   impact modifier means a polymer modifier added primarily to        alter the physical and mechanical properties of a thermoplastic        material and functioning by absorbing impact energy and        dissipating it in a nondestructive fashion; elastomers can be        used as impact modifiers, including but not limited to natural        rubbers, acrylics and styrenic elastomers, chlorinated        polyethylene, EVA copolymers, ethylene-propylene copolymers and        terpolymers, polybutadiene and polyisoprene;    -   thermal-stabilizing filler is a material which, when added to a        base resin, will decrease the resin's coefficient of thermal        expansion by at least 20 percent and increase the heat        deflection temperature by at least 20° C.;    -   toughness is determined using a notched Izod impact test        according to ASTM D256;    -   venting means the opening of the pressure relief vent of a cell;        and    -   vent pressure means the internal cell pressure at which the        pressure relief vent opens to release pressure from the cell.

Unless otherwise specified herein, all disclosed characteristics andranges are as determined at room temperature (20-25° C.), and boilingpoints are at one atmosphere pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross-sectional view of a cylindrical electrochemicalbattery cell, with one thermoplastic seal member between the can andcover and another thermoplastic seal member between the cover and ventball;

FIG. 2 is a cross-sectional view of a test membrane for a vaportransmission rate test; and

FIG. 3 is a graph showing creep strain as a function of time for threeresin types at 85° C., with an initial applied stress of 10,000 kPa.

DESCRIPTION

The invention will be better understood with reference to FIG. 1, whichshows an FR6 type cylindrical battery cell having a housing sealed bytwo thermoplastic seal members (a gasket and a vent bushing). Cell 10has a housing that includes a can 12 with a closed bottom and an opentop end that is closed with a cell cover 14 and a gasket 16. The can 12has a bead or reduced diameter step near the top end to support thegasket 16 and cover 14. The gasket 16 is compressed between the can 12and the cover 14 to seal an anode 18, a cathode 20 and electrolytewithin the cell 10. The anode 18, cathode 20 and a separator 26 arespirally wound together into an electrode assembly. The cathode 20 has ametal current collector 22, which extends from the top end of theelectrode assembly and is connected to the inner surface of the cover 14with a contact spring 24. The anode 18 is electrically connected to theinner surface of the can 12 by a metal tab (not shown). An insulatingcone 46 is located around the peripheral portion of the top of theelectrode assembly to prevent the cathode current collector 22 frommaking contact with the can 12, and contact between the bottom edge ofthe cathode 20 and the bottom of the can 12 is prevented by theinward-folded extension of the separator 26 and an electricallyinsulating bottom disc 44 positioned in the bottom of the can 12. Cell10 has a separate positive terminal cover 40, which is held in place bythe inwardly crimped top edge of the can 12 and the gasket 16. The can12 serves as the negative contact terminal. Disposed between theperipheral flange of the terminal cover 40 and the cell cover 14 is apositive temperature coefficient (PTC) device 42 that substantiallylimits the flow of current under abusive electrical conditions. Cell 10also includes a pressure relief vent. The cell cover 14 has an aperturecomprising an inward projecting central vent well 28 with a vent hole 30in the bottom of the well 28. The aperture is sealed by a vent ball 32and a thin-walled thermoplastic bushing 34, which is compressed betweenthe vertical wall of the vent well 28 and the periphery of the vent ball32. When the cell internal pressure exceeds a predetermined level, thevent ball 32, or both the ball 32 and bushing 34, are forced out of theaperture to release pressurized gases from the cell 10.

The materials used for cell components depend in part on the cell type,including the electrochemistry. For lithium and lithium ion cells, thereare many similarities in suitable materials.

The gasket comprises a thermoplastic material that is resistant to coldflow at high temperatures (e.g., 75° C. and above), chemically stable(resistant to degradation, e.g., by dissolving or cracking) when exposedto the internal environment of the cell and resistant to thetransmission of air gases into and electrolyte vapors from the cell.Gaskets can be made from thermoplastic resins. Resins used to makegaskets for nonaqueous cells can comprise polyphenylene sulfide andpolyphthalamide and combinations thereof as base resins. The base resinand can be blended with modifiers to provide the desired gasketproperties. Small amounts of other polymers, reinforcing inorganicfillers and/or organic compounds may also be added to the base resin ofthe gasket. A preferred base resin is polyphthalamide. In oneembodiment, polyphthalamide can be used alone. An example of a suitablepolyphthalamide resin is RTP 4000 from RTP Company, Winona, Minn., USA.In another embodiment an impact modifier is added to thepolyphthalamide. For example, 5 to 40 weight percent of an impactmodifier can be added; such a material is available as AMODEL® ET 1001 Lfrom Solvay Advanced Polymers, LLC, Alpharetta, Ga., USA. Anotherpreferred base resin is polyphenylene sulfide, to which from greaterthan 10 to no greater than 40, preferably from greater than 10 to nogreater than 30, and more preferably at least 15 weight percent of animpact modifier is added; such a material is available as FORTRON® SKX382 from Ticona-US, Summit, N.J., USA.

To maintain the desired compression of the gasket between the containerand cover, it is generally desirable to use gasket materials withrelatively low coefficients of thermal expansion to minimize the effectsof temperature. When the CTE is too high excessive overstress (resultingin excessive cold flow) can occur at high temperatures, and excessivecontraction can occur at low temperatures. It is also preferable for theCTE's of the container, cell cover and gasket to be relatively close toone another so that dimensions of their interface surfaces will changeby about the same amount in response to temperature changes, therebyminimizing the effects on gasket compression over a broad temperaturerange. The importance of the CTE's of the gasket, container and cellcover materials can be reduced by using a cell cover design like thatshown in FIG. 1, where the cover has a generally vertical wall that hassome radial spring characteristics.

Heat deflection temperature (HDT) is a measure of a resin's tendency tosoften when subjected to heat. The higher the HDT, the more rigid thematerial remains when heated. Preferably the resin used to make thegasket has an HDT of at least 50, preferably at least 75 and morepreferably at least 100° C. at a pressure of 18.56 kg/cm².

Creep strain rate is another measure of the material's tendency tosoften when subjected to heat. The lower the creep strain rate, the morerigid the material remains when heated. When the creep strain rate istoo high the material can flow excessively, resulting in a loss ofcompression of the gasket between the container and cell cover. Ideallythe average creep strain rate of the resin is zero. An average creepstrain rate of no greater than 0.01 percent/min. between 100 and 200minutes at 85° C. with a constant applied force of 6 N is preferred.More preferably the average creep strain rate is no more than about0.007 percent/min., and most preferably it is no more than about 0.004percent/min. Most preferably the average creep strain rate is no morethan 0.002 percent/min.

The gasket will also be resistant to the forces applied during and aftercell manufacturing, when the gasket is initially compressed, to preventdamage, such as cracks through which electrolyte can leak. Impactmodifiers can be included in the resin to increase the impact resistanceof the material.

To improve the seal at the interfaces between the gasket and the cellcontainer and the cell cover, the gasket can be coated with a suitablesealant material. A polymeric material such as EPDM can be used inembodiments with an organic electrolyte solvent.

The vapor transmission rates of water and the electrolyte solvent shouldalso be low to minimize the entry of water into the cell and loss ofelectrolyte from the cell. Water in the cell can react with the activematerials, and the internal resistance of the cell can increase to anundesirable level if too much electrolyte solvent is lost.

The vent bushing is a thermoplastic material that is resistant to coldflow at high temperatures (e.g., 75° C. and above). This can be achievedby including more than 10 weight percent, preferably at least 15percent, thermal-stabilizing filler in the thermoplastic material.Preferably no more than 40, more preferably no more than 30, weightpercent thermal-stabilizing filler is added. The base resin of thethermoplastic material is one that is compatible with the cellingredients (anode, cathode and electrolyte). The resin can beformulated to provide the desired sealing, venting and processingcharacteristics. The resin is modified by adding a thermal-stabilizingfiller to provide a vent bushing with the desired sealing and ventingcharacteristics at high temperatures.

Suitable polymeric resins include ethylene-tetrafluoroethylene,polybutylene terephthlate, polyphenylene sulfide, polyphthalamide,ethylene-chlorotrifluoroethylene, chlorotrifluoroethylene,perfluoroalkoxyalkane, fluorinated perfluoroethylene polypropylene andpolyetherether ketone. Ethylene-tetrafluoroethylene copolymer (ETFE),polyphenylene sulfide (PPS), polybutylene terephthalate (PBT) andpolyphthalamide (PPA) are preferred, especially for use in a cell withan electrolyte solvent containing a large percentage of highly volatile(high vapor pressure, low boiling point) ether compounds.

A suitable thermal-stabilizing filler is one which, when added to thethermoplastic resin, decreases the CTE of the resin by at least 20percent and increases the HDT of the resin by at least 20° C. Suchfillers may be inorganic materials, such as glass, clay, feldspar,graphite, mica, silica, talc and vermiculite, or they may be organicmaterials such as carbons. It may be advantageous for the fillerparticles to have a high average aspect ratio, such as fibers, whiskers,flakes and platelets.

Glass can be used as a thermal-stabilizing filler. A preferred type ofglass is E-glass. The lengths of the glass fibers will affect thematerial properties to some extent, particularly the thermal andmechanical properties, more so than the thermal expansion. The fiberlength can vary depending on the base resin use. For example, with PBTas the base resin, shorter fibers seem to work well, while with otherbase resins, longer fibers may be better. The glass fiber length can becontrolled in any suitable manner. In general, milling produces shorterfibers than chopping.

It is generally preferred that the wall of the vent bushing between thevent ball and the vent well in the cover be thin (e.g., 0.006 to 0.015inch as manufactured) and be compressed by about 25 to 40 percent whenthe bushing and ball are inserted into the cover.

The vent bushing can be manufactured using any suitable process.Injection molding is an example. Because the length of the glass fibersin the thermoplastic material can be reduced during injection molding ofthe vent bushings, the possible effects on the vent bushingcharacteristics should be considered before using reground scrap frommolding. The molding parameters used should be those that provide asmooth surface on the molded bushings (e.g., Society of the PlasticsIndustry Standard Surface Finish D3 or better). Molding parameters willvary with the type of material being molded. For TEFZEL® HT2004 (ETFEresin with 25 weight percent chopped glass filler, from E.I. du Pont deNemours and Company, Wilmington, Del., USA), a molding temperature ofabout 300° F. (149° C.) and a barrel temperature of about 680° F. (360°C.) has been found to work well with a fast (greater than about 2.5in./sec. (6.35 cm/sec.)) injection rate. Additives, such as impactmodifiers, may be used.

The mixture of base resin and filler used to make the vent bushingpreferably has a heat deflection temperature (HDT) of at least 90° C.(preferably at least 150° C. and more preferably at least 190° C.) and acoefficient of thermal expansion (CTE) between 50 and 90° C. of nogreater than 7.0×10⁻⁵ (preferably no greater than 5.0×10⁻⁵ and morepreferably no greater than 3.0×10⁻⁵) cm/cm/° C.

To maintain the desired compression of the bushing between the cover andvent ball, it is generally desirable to use materials for the ventbushing that have low coefficients of thermal expansion to minimize theeffects of temperature. When the CTE is greater than 5.0×10⁻⁵ cm/cm/°C., excessive overstress (resulting in excessive cold flow) can occur athigh temperatures and excessive contraction can occur at lowtemperatures. Both of these undesirable conditions can result ininsufficient compression in the vent bushing to provide a good sealagainst the cell cover and the vent ball, leading to loss of electrolytefrom the cell, water ingress into the cell and opening of the pressurerelief vent under normal storage and use conditions.

It is also preferable for the CTE's of the cell cover, vent ball andvent bushing to be close to one another so that dimensions of the cover,ball and bushing interface surfaces will change by about the same amountin response to temperature changes, thereby minimizing the effects onbushing compression over a broad temperature range.

The heat deflection temperature is a measure of the material's tendencyto soften when subjected to heat. The higher the temperature, the morerigid the material remains when exposed to heat. When the HDT is too lowthe material can flow excessively at high temperatures, resulting in aloss of compression of the vent bushing between the cell cover and thevent ball.

The vapor transmission rates of water and the electrolyte solvent shouldalso be low to minimize the entry of water into the cell and loss ofelectrolyte from the cell. Water in the cell can react with the activematerials, and the internal resistance of the cell can increase to anundesirable level if too much electrolyte solvent is lost.

The cell container is often a metal can with an integral closed bottom,though a metal tube that is initially open at both ends may also be usedinstead of a can. The can is generally steel, plated with nickel on atleast the outside to protect the outside of the can from corrosion. Thetype of plating can be varied to provide varying degrees of corrosionresistance or to provide the desired appearance. The type of steel willdepend in part on the manner in which the container is formed. For drawncans the steel can be a diffusion annealed, low carbon, aluminum killed,SAE 1006 or equivalent steel, with a grain size of ASTM 9 to 11 andequiaxed to slightly elongated grain shape. Other steels, such asstainless steels, can be used to meet special needs. For example, whenthe can is in electrical contact with the cathode, a stainless steel maybe used for improved resistance to corrosion by the cathode andelectrolyte.

The cell cover is typically metal. Nickel plated steel may be used, buta stainless steel is often desirable, especially when the cover is inelectrical contact with the cathode. The complexity of the cover shapewill also be a factor in material selection. The cell cover may have asimple shape, such as a thick, flat disk, or it may have a more complexshape, such as the cover shown in FIG. 1. When the cover has a complexshape like that in FIG. 1, a type 304 soft annealed stainless steel withASTM 8-9 grain size may be used, to provide the desired corrosionresistance and ease of metal forming. Formed covers may also be plated,with nickel for example.

The terminal cover should have good resistance to corrosion by water inthe ambient environment, good electrical conductivity and, when visibleon consumer batteries, an attractive appearance. Terminal covers areoften made from nickel plated cold rolled steel or steel that is nickelplated after the covers are formed. Where terminals are located overpressure relief vents, the terminal covers generally have one or moreholes to facilitate cell venting.

The vent ball can be made from any suitable material that is stable incontact with the cell contents and provides the desired cell sealing andventing characteristic. Glasses or metals, such as stainless steel, canbe used. The vent ball should be highly spherical and have a smoothsurface finish with no imperfections, such as gouges, scratches or holesvisible under 10 times magnification. The desired sphericity and surfacefinish depend in part on the ball diameter. For example, in oneembodiment of a Li/FeS₂ cell, for balls about 0.090 inch (2.286 mm) indiameter the preferred maximum sphericity is 0.0001 inch (0.00254 mm)and the preferred surface finish is 3 microinches (0.0762 μm) RMSmaximum. For balls about 0.063 inch (1.600 mm) in diameter, thepreferred maximum sphericity is 0.000025 inch (0.000635 mm), and thepreferred maximum surface finish is 2 microinches (0.0508 μm) RMS.

In one embodiment of an FR6 Li/FeS₂ cell according to FIG. 1, theupstanding side wall of the gasket is 0.0205 inch (0.521 mm) thick asmanufactured. The diameters of the cell cover, gasket and crimped canare such that the gasket is compressed by about 30 percent of itsoriginal thickness to provide a good seal. The gasket is preferablycoated with a sealant such as ethylene propylene diene terpolymer(EPDM), but other suitable sealant materials can be used. The initialvent bushing wall thickness is 0.0115 inch (0.292 mm). It is compressedby about 30 to 35 percent of its original thickness in the sealed cell.A sealant could be used between the vent bushing and the cell cover orbetween the vent bushing and the vent ball, or a sealant could beapplied over the cover, bushing and ball to improve the seal, butpreferably no sealant is used in order to avoid adversely affecting cellventing or the vent pressure.

An anode for a lithium cell contains lithium metal, often in the form ofa sheet or foil. The composition of the lithium can vary, though thepurity is always high. The lithium can be alloyed with other metals,such as aluminum, to provide the desired cell electrical performance.When the anode is a solid piece of lithium, a separate current collectorwithin the anode is generally not used, since the lithium metal has avery high electrical conductivity. However, a separate current collectorcan be used to provide electrical contact to more of the remaininglithium toward the end of cell discharge. Copper is often used becauseof its conductivity, but other conductive metals can be used as long asthey are stable inside the cell.

An anode for a lithium ion cell includes one or morelithium-intercalable materials (capable of insertion and deinsertion oflithium ions into their crystalline structure). Examples of suitablematerials include, but are not limited to carbons (e.g., graphitic,mesophase and/or amorphous carbons), transition metal oxides (e.g.,those of nickel, cobalt and/or manganese), transition metal sulfides(e.g., those of iron, molybdenum, copper and titanium) and amorphousmetal oxides (e.g., those containing silicon and/or tin). Thesematerials are generally particulate materials that are formed into thedesired shape. Conductive materials such as metal, graphite and carbonblack powders may be added to improve electrical conductivity. Bindersmay be used to hold the particulate materials together, especially incells larger than button size. Small amounts of various additives mayalso be used to enhance processing and cell performance. The anodegenerally includes a current collector; copper is a common choice. Thecurrent collector may be a thin metal foil sheet, a metal screen, anexpanded metal or one or more wires. The anode mixture (active materialand other ingredients) can be combined with the current collector in anysuitable manner. Coating and embedding are examples.

Because lithium and lithium alloy metals are typically highlyconductive, a separate current collector within the anode is oftenunnecessary in lithium and lithium alloy anodes. When an anode currentcollector is required, as is often the case in lithium ion cells, thecurrent collector can be made from a copper or copper alloy metal.

A cathode for a lithium cell contains one or more active materials,usually in particulate form. Any suitable active cathode material may beused. Examples include FeS₂, MnO₂, CF_(x) and (CF)_(n).

A cathode for a lithium ion cell contains one or morelithium-intercalated or lithium-intercalable active materials, usuallyin particulate form. Any suitable active lithium-intercalated orlithium-intercalable material may be used, alone or in combination withothers. Examples include metal oxides (e.g., those of vanadium andtungsten), lithiated transition metal oxides (e.g., those includingnickel, cobalt and/or manganese), lithiated metal sulfides (e.g., thoseof iron, molybdenum, copper and titanium) and lithiated carbons.

In addition to the active material, a cathode for a lithium or lithiumion cell often contains one or more conductive materials such as metal,graphite and carbon black powders. A binder may be used to hold theparticulate materials together, especially for cells larger than buttonsize. Small amounts of various additives may also be used to enhanceprocessing and cell performance.

A cathode current collector may be required. Aluminum is a commonly usedmaterial.

Any suitable separator material may be used. Suitable separatormaterials are ion-permeable and electrically nonconductive. They aregenerally capable of holding at least some electrolyte within the poresof the separator. Suitable separator materials are also strong enough towithstand cell manufacturing and pressure that may be exerted on themduring cell discharge without tears, splits, holes or other gapsdeveloping. Examples of suitable separators include microporousmembranes made from materials such as polypropylene, polyethylene andultrahigh molecular weight polyethylene. Preferred separator materialsfor Li/FeS₂ cells include CELGARD® 2400 microporous polypropylenemembrane (from Celgard Inc., Charlotte, N.C., USA) and Tonen ChemicalCorp.'s Setella F20DHI microporous polyethylene membrane (available fromExxonMobile Chemical Co, Macedonia, N.Y., USA). A layer of a solidelectrolyte or a polymer electrolyte can also be used as a separator.

Electrolytes for lithium and lithium ion cells are nonaqueouselectrolytes. In other words, they contain water only in very smallquantities (e.g., no more than about 500 parts per million by weight,depending on the electrolyte salt being used) as a contaminant. Suitablenonaqueous electrolytes contain one or more electrolyte salts dissolvedin an organic solvent. Any suitable salt may be used, depending on theanode and cathode active materials and the desired cell performance.Examples include lithium bromide, lithium perchlorate, lithiumhexafluorophosphate, potassium hexafluorophosphate, lithiumhexafluoroarsenate, lithium trifluoromethanesulfonate and lithiumiodide. Suitable organic solvents include one or more of the following:dimethyl carbonate, diethyl carbonate, methylethyl carbonate, ethylenecarbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylenecarbonate, methyl formate, γ-butyrolactone, sulfolane, acetonitrile,3,5-dimethylisoxazole, n,n-dimethyl formamide and ethers. Thesalt/solvent combination will provide sufficient electrolytic andelectrical conductivity to meet the cell discharge requirements over thedesired temperature range. While the electrical conductivity isrelatively high compared to some other common solvents, ethers are oftendesirable because of their generally low viscosity, good wettingcapability, good low temperature discharge performance and good highrate discharge performance. This is particularly true in Li/FeS₂ cellsbecause the ethers are more stable than with MnO₂ cathodes, so higherether levels can be used. Suitable ethers include, but are not limitedto acyclic ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane,di(methoxyethyl)ether, triglyme, tetraglyme and diethyl ether; andcyclic ethers such as 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran and 3-methyl-2-oxazolidinone.

Specific anode, cathode and electrolyte compositions and amounts can beadjusted to provide the desired cell manufacturing, performance andstorage characteristics.

The invention is particularly useful for cells having electrolytesolvents with a very high level (e.g., a total of at least 80 volumepercent) of ethers with very low boiling points (e.g., no greater than90° C. at sea level). The advantage is even greater when the volumepercent of ethers in the solvent is at least 90 percent, and even moreso with at least 98 volume percent ethers in the solvent.

The cell can be closed and sealed using any suitable process. Suchprocesses may include, but are not limited to, crimping, redrawing,colleting and combinations thereof. For example, for the cell in FIG. 1,a bead is formed in the can after the electrodes and insulator cone areinserted, and the gasket and cover assembly (including the cell cover,contact spring and vent bushing) are placed in the open end of the can.The cell is supported at the bead while the gasket and cover assemblyare pushed downward against the bead. The diameter of the top of the canabove the bead is reduced with a segmented collet to hold the gasket andcover assembly in place in the cell. After electrolyte is dispensed intothe cell through the apertures in the vent bushing and cover, a ventball is inserted into the bushing to seal the aperture in the cellcover. A PTC device and a terminal cover are placed onto the cell overthe cell cover, and the top edge of the can is bent inward with acrimping die to hold retain the gasket, cover assembly, PTC device andterminal cover and complete the sealing of the open end of the can bythe gasket.

The above description is particularly relevant to FR6 type cylindricalLi/FeS₂ cells with nonaqueous electrolytes and to pressure relief ventscomprising a thermoplastic bushing and vent ball. However, the inventionmay also be adapted to other types of cells, such as non-cylindrical(e.g., prismatic) cells, cells with other active materials, cells withother electrolyte solvents (e.g., water) and cells with other pressurerelief vent designs. For example, the aperture and pressure relief ventcan be located in a cell cover or the container. The aperture can bedefined by a uniform opening, such a straight cylindrical opening, or itmay be nonuniform, with a reduced diameter opening in one section, suchas the aperture in the cell cover in FIG. 1. The seal member sealing theaperture in the housing can be a thermoplastic plug, or it can be abushing into which a plug is inserted. The plug can be of any suitablesolid shape, including but not limited to, a sphere, an ellipsoid, anovoid and a cylinder. Cells according to the invention can have spiralwound electrode assemblies such as that shown in FIG. 1, anotherelectrode configuration, such as folded strips, stacked flat plates,bobbins and the like.

The invention and its features and advantages are further illustrated inthe following examples.

EXAMPLE 1

Gaskets for FR6 type cells similar to the gasket shown in FIG. 1 wereinjection molded from polypropylene homopolymer (PROFAX° 6524),polybutylene terephthlate (VALOX® 310), ethylene tetrafluoroethylenecopolymer (TEFZEL® 2185), polyphenylene sulfide with 15 weight percentimpact modifier (FORTRON® SKX 382) and polyphthalamide with 10-30 weightpercent impact modifier (AMODEL(® ET 1001 L) and are referred to belowas PP, PBT, ETFE, PPS and PPA gaskets, respectively.

EXAMPLE 2

FR6 type Li/FeS₂ cells were made according to FIG. 1 and the abovedescription, except that the cell covers (14) did not have vent holes(30), so vent bushings and vent balls were not used. Cells were madewith PP, PBT, ETFE, PPS and PPA gaskets from Example 1. The cells hadthe following features (quantitative values are design averages):

-   -   can material—diffusion annealed, low carbon, aluminum killed,        SAE 1006 steel, ASTM 9 to 11 grain size, equiaxed to slightly        elongated shape; nickel plated; about 0.010 inch (0.254 mm)        thick, to provide a 0.0095 inch (0.241 mm) thick can wall;    -   can CTE about 1.25×10⁻⁵ cm/cm/° C.;    -   cell cover material—0.013 inch (0.330 mm) thick type 304 soft        annealed stainless steel; ASTM 8-9 grain size; post-plated with        nickel;    -   cell cover CTE—1.72×10⁻⁵ cm/cm/° C.;    -   cell cover vent well inside diameter—0.105 inch (2.67 mm);    -   gasket wall thickness—0.0205 inch (0.521 mm);    -   gasket sealant coating material—EPDM with 56% ethylene and 9%        diene;    -   gasket compression—about 32 percent of the initial gasket wall        thickness;    -   electrolyte composition—9.14 weight percent LiI solute in a        solvent blend of 63.05 weight percent DIOX, 27.63 weight percent        DME and 0.18 weight percent DMI (65:35:0.2 by volume);    -   electrolyte quantity—1.6 g; and    -   cell internal void volume—10 percent.

EXAMPLE 3

Cells from Example 2 made with each of the gasket types were tested todetermine the amount of weight loss during storage at reduced pressurefollowed by thermal shock. Some cells with each gasket type were testedin an upright orientation (as shown in FIG. 1), and others wereinverted.

Cells were first stored for about 6 hours at room temperature and apressure of about 11.6 kPa; weight loss was not significant. In thethermal shock portion of the test, cells were stored for 6 hours at 75°C., followed by storage for 6 hours at −40° C.; this was repeated 10times, with no more than 30 minutes between the test temperatureextremes; after temperature cycling the cells were stored for 24 hoursat room temperature. For three of the gasket types (PP, PPS and PPA),three lots of cells, made at different times, were tested; for the othertwo gasket types (PBT and ETFE), only one lot of each was made andtested. The change in mass was determined for each cell. The averageweight loss results are summarized in Table 1 for each cell lot. Theaverage weight loss was better for cells with PBT, ETFE, PPS and PPAgaskets than for cells with PP gaskets, with cells made with PBT and PPAgaskets being the best overall. There was no substantial difference inaverage weight loss due to cell orientation during the test. TABLE 1Gasket Type PP PBT ETFE PPS PPA Average 0.0081 — — 0.0099 0.0000 Weight0.0079 — 0.0032 0.0104 0.0012 Loss (g) 0.0090 0.0010 — 0.0059 0.0010

EXAMPLE 4

Cells from Example 3 were stored for 3 weeks at 85° C. and then weighedto determine the amount of additional weight loss after storage at 85°C. Some cells were stored in an upright orientation (as shown in FIG.1), and others were inverted. The average weight losses are shown foreach lot of cells with PP, ETFE and PPA gaskets in Table 2. The averageadditional weight loss was significantly less for cells with ETFE, PPSand PPA gaskets than for cells with PP gaskets. Some of the cells witheach gasket type were autopsied and examined. The PBT gaskets had crackson the surfaces that had been exposed to the electrolyte in the cells,indicating degradation of the material. TABLE 2 Gasket Type PP ETFE PPSPPA Average 0.0700 — 0.0328 0.0018 Weight 0.0748 0.0093 0.0368 0.0005Loss (g)

EXAMPLE 5

Gaskets made with different grades of PBT were submerged in varioussolutions at 70° C. and examined periodically to determine the source ofthe cracking observed in Example 4. The results are summarized in Table3; “fail” indicates cracking after 7 days or less, and “pass” indicatesno cracking after 60 days. Gaskets with all PBT grades tested failedwhen tested in the electrolyte used in the cells in Example 2. Gasketsdid not fail when tested in solutions that did not contain both lithiumand iodide ions in a nonaqueous solvent. TABLE 3 Solute Type andConcentration Solvent (moles/liter Components and Gasket solvent) VolumeRatio Material Results LiI DIOX:DME:DMI VALOX ® fail 0.75 65:35:0.2 310LiI DIOX:DME:DMI CELANEX ® fail 0.75 65:35:0.2 1600A LiI DIOX:DME:DMIVALOX ® fail 0.75 65:35:0.2 HR326 LiI DIOX:DME CELANEX ® fail 0.75 65:351600A none DIOX:DME:DMI VALOX ® pass 65:35:0.2 310 none DIOX:DME:DMICELANEX ® pass 65:35:0.2 1600A LiCF₃SO₃ DIOX:DME:DMI CELANEX ® pass 1.065:35:0.2 1600A KI DIOX:DME:DMI CELANEX ® pass saturated 65:35:0.2 1600ANaI DIOX:DME:DMI CELANEX ® pass 0.75 65:35:0.2 1600A LiI distilled waterCELANEX ® pass 0.75 1600A

EXAMPLE 6

Tables 5 and 6 show properties of materials used in Example 1. Table 5shows typical CTE, HDT and toughness characteristics for the grades ofPP, PBT, PPS and PPA shown, where available. TABLE 3 HDT at 18.56Material Material CTE kg/cm² Toughness Type Grade (cm/cm/° C.) × 10⁻⁵ (°C.) (Joules/m) PP PRO-FAX ® — —  37 6524 PBT VALOX ® 8.1 54  54 310 ETFETEFZEL ® 12.6 74 (no break) HT2185 PPS FORTRON ® 8.4 82 507 SKX 382 PPAAMODEL ® 7.5 120 960 ET 1001 L

Table 6 shows the vapor transmission rates (VTR) of water and thedesired organic electrolyte (9.14 wt % LiI solute in a solvent blend of63.05 wt % 1,3-dioxolane, 27.63 wt % 1,2-dimethoxyethane and 0.18 wt %3,5-dimethylisoxazole) through a number of thermoplastic materials atroom temperature (RT), 60° C. and 75° C. The vapor transmission rateswere determined using the following method, adapted from ASTM E96-80(Standard Test Method for Water Vapor Transmission of Materials):

-   -   1. mold a thermoplastic test membrane according to the membrane        100 in FIG. 2, where the height, outside diameter and inside        diameter at wall 101 are suitable for providing a seal between        the bottle and seal in steps 2 and 5 below, the membrane        thickness between wall 101 and hub 103 is 0.020 inch (0.508 mm)        and the test surface area (step 9 is the surface area of the        membrane between wall 101 and hub 103 [for the serum bottle and        seal described in the examples in steps 2 and 5 below, a        suitable test membrane has a wall outside diameter of 0.770 inch        (19.56 mm), a wall inside diameter of 0.564 inch (14.33 mm), a        hub diameter of 0.127 inch (3.23 mm), a hub length of 0.075 inch        (1.91 mm) below the lower test surface and a test surface area        of 0.237 in.² (1.529 cm²)];    -   2. put about 8 ml of liquid (water or electrolyte) into a 15 ml        bottle (e.g., Wheaton Serum Bottle, 25 mm diameter×54 mm high,        Cat. No. 06-406D);    -   3. apply sealant (e.g., G.E. Silicone II for testing at up to        60° C.; vacuum grease for testing at up to 75° C.) to the lip of        the bottle;    -   4. place the test membrane over the top of the bottle;    -   5. place a seal with a ⅝ inch (15.88 mm) diameter center hole        (e.g., Wheaton Aluminum Seal Cat. No. 060405-15) over the test        membrane and crimp the seal tightly onto the bottle;    -   6. weigh the sealed bottle;    -   7. store the bottle at the desired test temperature and reweigh        (at room temperature) at regular intervals (e.g., monthly for 6        months at room temperature; daily for 2 weeks at 60° C. and 75°        C.);    -   8. determine the total weight loss (use a negative value to        indicate a weight gain) over the test period;    -   9. calculate the vapor transmission rate in g·0.001 in./day·100        in.² (g·0.0254 mm/day·0.65416 cm²) using the average total        weight loss from step 8 (excluding any individual samples that        are extremely high due to loss of seal) and the formula [(ave.        weight loss in grams/day)(membrane thickness in        inches/1000)(100)/(test surface area of membrane)], where day=24        hours; and    -   10. perform steps 2-9 on an empty bottle, and correct the        calculated vapor transmission rate for the test liquid by        subtracting the result from step 9 for the empty bottle from the        result from step 9 for the bottle containing the test liquid.

The PP material had the lowest water vapor transmission rate at roomtemperature, but its electrolyte vapor transmission rate at 60° C. and75° C. was much higher than any of the others. The electrolyte vaportransmission rates for the PPS and PPA materials were substantiallylower than those of PBT and ETFE. TABLE 6 VTR (g · 0.0254 mm/day ·0.65416 cm²) Material Material Water Electrolyte Type Grade RT 60° C.75° C. RT 60° C. 75° C. PP PRO-FAX ® 0.2 7 18 8 437 1394 6524 PBTVALOX ® 1 11 35 4 129 372 310 ETFE TEFZEL ® 0.6 7 20 6 140 314 HT2185PPS FORTRON ® 0.5 4 9 — 15 97 SKX 382 PPA AMODEL ® 0.7 10 29 — 59 120 ET1001 L

EXAMPLE 7

Test samples made from the PP, PPS and PPA resins used in Example 1 weretested at 85° C. to determine the tensile creep strain rate of thoseresins. The testing was done using a Tritec 2000 DMA (TritonTechnologies, Ltd., UK). The test samples were made by compressionmolding the virgin resin to form a 0.25 mm thick film and then cuttingindividual samples 2.3 mm wide. An initial gauge length of 2.0 mm wasused, and a constant tensile force of 6 N (tensile stress of 10,000 kPa)was applied. The results are plotted in the graph in FIG. 3, which showsthe percent creep stain as a function of time. After application of theinitial tensile stress, a flat line indicates a creep strain rate ofzero (i.e., no material flow). The average creep strain rate for a giventime interval (e.g., between 100 and 200 minutes) is calculated bysubtracting the creep strain at 100 min. from the creep strain at 200min. and dividing the difference by 100 min. The creep strain values at100 and 200 minutes and the average creep strain rate are shown in Table7. The average creep strain rates of the PPS and PPA materials weresubstantially better than that of PP, with PPA being the best. TABLE 7Creep Strain Creep Strain Ave. Creep Material Material at at Strain RateType Grade 100 min. (%) 200 min. (%) (%/min.) × 10⁻³ PP PRO-FAX ® 41.743.2 15 6524 PPS FORTRON ® 2.9 3.2 3 SKX 382 PPA AMODEL ® 7.4 7.4 0 ET1001 L

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the preferred versions containedherein.

Each feature disclosed in this specification (including the accompanyingclaims, abstract, and drawings) is one example only of a generic seriesof equivalent or similar features, and each of the features disclosedmay be replaced by alternative features serving the same, equivalent orsimilar purpose, unless expressly stated otherwise.

1. An electrochemical battery cell comprising: a housing comprising ametal container with at least one open end and at least a first metalcover disposed in the at least one open end of the container; a positiveelectrode; a negative electrode; a separator disposed between thepositive and negative electrodes; an electrolyte; and a thermoplasticseal member made from a polymeric resin comprising at least one memberselected from the group consisting of polyphenylene sulfide blended withfrom greater than 10 to no greater than 40 weight percent of an impactmodifier and polyphthalamide.
 2. The cell as defined in claim 1, whereinthe resin comprises polyphthalamide.
 3. The cell as defined in claim 2,wherein the polyphthalamide is blended with an impact modifier.
 4. Thecell as defined in claim 3, wherein the resin comprises 5 to 40 weightpercent of the impact modifier.
 5. The cell as defined in claim 1,wherein the resin comprises polyphenylene sulfide blended with at least15 weight percent of an impact modifier.
 6. The cell as defined in claim1, wherein the electrolyte is a nonaqueous electrolyte.
 7. The cell asdefined in claim 6, wherein the electrolyte comprises an organicsolvent.
 8. The cell as defined in claim 6, wherein the electrolytecomprises a solute comprising lithium and iodide ions.
 9. The cell asdefined in claim 8, wherein the solute comprises lithium iodide.
 10. Thecell as defined in claim 6, wherein the organic solvent comprises atleast one ether compound.
 11. The cell as defined in claim 10, whereinthe organic solvent comprises at least 80 volume percent of one or moreethers each having a boiling point no greater than 90° C.
 12. The cellas defined in claim 6, wherein the negative electrode comprises at leastone member of the group consisting of lithium, a lithium alloy and alithium intercalation compound.
 13. The cell as defined in claim 6,wherein the positive electrode comprises at least one member of thegroup consisting of iron disulfide, manganese dioxide and a lithiumintercalation compound.
 14. The cell as defined in claim 1, wherein theat least one thermoplastic seal member is disposed between the containerand the first metal cover.
 15. The cell as defined in claim 1, whereinthe resin has an average creep strain rate, at 85° C., between 100 and200 minutes after application of a constant tensile stress of 10,000kPa, of no greater than 0.002 percent per minute.
 16. The cell asdefined in claim 1, wherein the at least one thermoplastic seal membercomprises a first seal member, disposed between the container and thefirst cover, and a second seal member, disposed in an aperture in thefirst metal cover.
 17. The cell as defined in claim 16, wherein thepolymeric resin from which the second seal member is made furthercomprises greater than 10 weight percent of a thermal-stabilizingfiller.
 18. The cell as defined in claim 17, wherein the polymeric resinfrom which the second seal member is made comprises polyphthalamide. 19.An electrochemical battery cell comprising: a housing comprising a metalcontainer with an open end and a metal cover disposed in the open end ofthe container; a positive electrode; a negative electrode; a separatordisposed between the positive and negative electrodes; an electrolytecomprising a solute dissolved in a nonaqueous organic solvent, thesolute comprising lithium and iodide ions; and a thermoplastic sealmember disposed between the metal container and the metal cover; whereinthe thermoplastic seal member is made from a polymeric resin comprisingat least one member selected from the group consisting of polyphenylenesulfide blended with from greater than 10 to no greater than 40 weightpercent of an impact modifier and polyphthalamide.
 20. The cell asdefined in claim 19, wherein the lithium iodide is dissolved in asolvent comprising at least 80 volume percent of one or more ethers,each having a boiling point no greater than 90° C.
 21. The cell asdefined in claim 20, wherein the negative electrode comprises a lithiumalloy and the positive electrode comprises iron disulfide.
 22. The cellas defined in claim 19, wherein the resin comprises polyphthalamideblended with an impact modifier.
 23. The cell as defined in claim 22,wherein the resin comprises 5 to 40 weight percent of the impactmodifier.
 24. The cell as defined in claim 19, wherein the resincomprises polyphenylene sulfide blended with at least 15 weight percentimpact modifier.
 25. An electrochemical battery cell comprising: ahousing comprising a metal container with an open end and a metal coverdisposed in the open end of the container; a positive electrodecomprising iron disulfide; a negative electrode comprising metalliclithium; a separator disposed between the positive and negativeelectrodes; an electrolyte comprising a solute dissolved in a nonaqueousorganic solvent, the solute comprising lithium and iodide ions, and thesolvent comprising at least 80 volume percent of one or more ethers,each having a boiling point no greater than 90° C.; and a thermoplasticseal member disposed between the metal container and the metal cover,wherein the thermoplastic seal member is made from a polymeric resincomprising at least one member selected from the group consisting ofpolyphenylene sulfide blended with from greater than 10 to no greaterthan 40 weight percent of an impact modifier and polyphthalamide. 26.The cell as defined in claim 25, wherein the solute comprises lithiumiodide.